Tuesday, October 29, 2013

A Who's Who of WDIs

Recently I received an inquiry from a Texas pest control company wanting to know if there was a list of official wood destroying insects (WDIs) in Texas. Since there are some specific instructions in state regulations governing WDI inspections, you would be excused for thinking that there might be an official list. But if there is, I can't find it.  If you go to the relevant section of the Texas Administrative Code, the rules say "The purpose of the [WDI] inspection is to provide a report regarding the absence or presence of wood destroying insects and conditions conducive to wood destroying insect infestation."  However, the rules don't specifically define what consists of a WDI.

So in lieu of any official list, here is my list of the important WDIs in Texas.  If you're from another state, the list is likely to be similar, although the relative importance of each of these pests varies from region to region.
Termite wings provide good diagnostic clues to the type of
termites infesting a home. Reticulitermes wings are smooth,
without hairs, and have two heavier veins along the leading
edge of the forewing.
  • Subterranean termites (Reticulitermes species. Note: when the word "species" is written after the genus name, it refers to multiple different species within the genus). Knowing the exact species is not important for a professional doing an inspection, but keep in mind that there may be some differences (e.g., swarming times or potential for destruction) among the different termite species.  The most economically important termite species in Texas, and the U.S., is Reticulitermes flavipes, the eastern subterranean termite. These termites are called "subterranean" because they need contact with the soil, and almost always maintain their nest underground while foraging on both underground and above-ground wood.  Inspections should focus on looking for alates (swarmers) and the presence of mud tubes extending from the soil into the structure.  Alates can be confirmed as Reticulitermes by their forewings, which bear two strong, dark veins along the leading edge.  Wood damage from this and other Reticulitermes species consists of galleries chewed into the spring wood, following the growth rings. Also, because they are subterranean, gallery walls will be covered with specks of "mud", a combination of feces, saliva and soil.  
  • Formosan alate wings are covered with fine hairs, visible
    under magnification.
    Drywood termite wings are often dusky and have at least
    three strong veins along the leading edge of the forewing.
  • Formosan subterranean termites Coptotermes formosanus. This is an exotic termite species that has established in parts of Texas, but is also found in other parts of the South and in parts of California. One of the principal means of its spread appears to be via recycled railroad ties.  The Formosan termite belongs to the same family as Reticulitermes termites, and shares some of the same characteristics, including subterranean nests and mud spattered galleries; hence, it is also technically a "subterranean" termite. Identify Coptotermes by its nighttime swarming habits and its large, yellowish-colored alate.  The wing veination is similar to Reticulitermes, but the wing membranes are covered with fine hairs.  Workers are not easily distinguished from our other subterranean species, but soldiers have a teardrop-shaped head, contrasted with the rectangular head of Reticulitermes workers.  Galleries are similar to other subterranean termites, but Formosan termites produce "carton", a dense, honeycombed structure made from mud and wood pulp cemented together with saliva and feces.  
  • Drywood termites (Cryptotermes and Incistitermes species) The so-called drywood termites are distinguished from subterranean termites by their above-ground nests and lack of contact with the soil. Because they live in wood, which usually has lower moisture content than soil, drywood termites are very efficient conservers of water. The most obvious sign of this skill are the fecal pellets they produce. Unlike the wet, smeared feces of subterranean termites, drywood feces are hard, dry pellets.  In the drywood termite rectum all water is squeezed from the feces by six rectal pads, leaving small (1/32 inch-long), six-sided pellets. Finding these pellets is hard proof of a drywood termite infestation. In addition, drywood termite galleries do not follow the grain of the wood, but may extend across multiple annual rings. Alates fly at night and have three strong, dark veins at the leading edge of the forewing. Drywood termites are most common in warm, high-humidity regions, such as the Gulf coastal areas, and parts of southern California.  They may be found in other parts of the country, however, when brought in on furniture or infested lumber. 
    Lyctid powderpost beetle adults (left) are distinguished from
    the common pantry pest, red flour beetle (right), by their
    round eyes and two-segmented antennae.  
  • Lyctid powderpost beetles (family Bostrichidae, subfamily Lyctinae). These small, cylindrical beetles are usually brought into homes in infested hardwood trim or flooring, or in infested furniture. They are one of the most important WDIs in Texas. If you're not in the habit of looking carefully for signs of these beetles during a WDI inspection, you're opening your business up to a potential legal mess. The presence of these beetles in new homes has become highly litigious, as the owners look for someone to blame for their new, beetle-infested home. It's critical to look carefully at all hardwood trim, including wainscoting, baseboards, windowsills, cabinetry and wood flooring.  On horizontal floors or trim, sawdust usually accumulates in volcano-like piles surrounding the adult beetle emergence hole.  On vertical wood, small piles of very fine, almost silky, frass will accumulate on cabinets, edges or floors underneath the emergence hole. Adults can be distinguished from the similar-appearing red flour beetle by their darker color; globular, protruding eyes; 2-segmented antennal club and enlarged hind coxae.   
  • Carpenter ants are easily identified by their large size, single
    node between abdomen and thorax, and smoothly rounded
    thoracic profile.  Many Texas species are bi-colored, like this
    specimen; but color alone can be misleading.
  • Carpenter ants (Campanotus species). This insect is usually listed as a WDI; however in Texas carpenter ants are not very likely to do structural damage. They are more likely to occur in small colonies in wall voids and in insulation, but rarely as destroyers of sound wood. Some species of carpenter ant, like C. modoc and C. pennsylvanicus, are well-known wood destroyers, especially in the Pacific Northwest and in the northeastern states. They have given all carpenter ants a reputation as wood destroyers. For this reason, and because they are not difficult to report, I would recommend including carpenter ant evidence on a WDI inspection report.  The similarly-colored (but physically very different) acrobat ant, is not reported to eat or damage wood, therefore I would not report it as a WDI.  Carpenter ants are relatively easily identified by their large size, polymorphism (different sized workers in the same colony), single node and smooth curved thoracic profile. Inspectors should also be on the lookout for carpenter ant frass, which is the colony's trash dump.  Frass piles may include wood, insulation, dead insects, and sometimes pupal cases.  Any unusual debris piles that contain insect fragments are likely carpenter ants.
  • The old house borer is a medium-sized beetle (0.6 to 1 inch)
    with two raised bumps and a mustache-shaped ridge on
    the pronotum (shield behind head).
  • Old House borer (Hylotrupes bajulus). The round-headed borer family, to which the old house borer (OHB) belongs, consists mostly of larger beetles with long antennae.  Most infest only dying or recently killed trees, so pose little long-term threat to a structure (although they may emerge from infested wood in the first year or so of a new home).  The OHB is an exception to the low-threat rule because of its ability to re-infest homes after its first emergence. Most infestations occur in homes up to 10 years old, but they can also infest and re-infest older homes.  According to Dr. Harry Moore, retired WDI expert from North Carolina State University, the OHB prefers wood with moisture content between 15 and 25%.  This moisture level is higher than normal in all but the more humid parts of the country.  Adult beetles are distinctive, emergence holes are oval in shape and 1/4 to 1/3 inch maximum diameter. Frass consists of very fine powder and tiny, elongate, blunt-ended pellets.  Infestations of OHB are most common in the humid Piedmont areas of the mid-Atlantic seaboard; however they can be found in homes throughout the eastern U.S.  Infestations are relatively rare in Texas.
  • Bostrichid beetles are mostly a minor WDI pest.  The rasp-like
    pronotum and cylindrical body with abruptly angled wing
    tips are characteristic of this family.
  • Anobiid and other Bostrichid beetles.  Any emergence holes in structural wood or trim, of course, should be reported on a WDI report.  However, when the other pests listed above are ruled out, most of the remaining culprits will belong to miscellaneous species of anobiid (ANN oh BEE id) and bostrichid (boss STRICK id) beetles. Nationwide, anobiid beetles are the more important group.  These beetles feed on sapwood of both hard- and soft-woods.  They leave circular exit holes 1/16 to 1/8 inch in diameter, and produce a fine powdery frass with conspicuous pellets.  Adults of these beetles are relatives of the cigarette beetle and have a similar with a oval to cylindrical shape and downward pointing head, hidden from above.  Anobiid beetles thrive in wood with higher moisture content (15-30%) and probably for this reason, infestations in Texas are uncommon except in damp crawl spaces.  Some of the smaller holes bored by anobiid beetles may be confused with Lyctid powderpost beetles, but the frass is distinguished by the presence of rough pellets.
         Bostrichid beetles (with the exception of the Lyctid powderpost beetles) are generally incapable of re-infesting wood. Holes made by emerging adults are round and 3/32 to 9/32 inch in diameter.  Frass is tightly packed inside tunnels and tends to stick together.  Most bostrichid beetles have several rasp-like teeth on the front of the pronotum, presumably to aid in collecting and packing frass in the galleries.  One of the most common ways bostrichid beetles are introduced into homes is via wicker baskets and furniture.

No comments: